The present invention relates to a multifunction acoustic device used in a portable instrument such as a portable telephone.
There has been provided an acoustic device of the portable instrument in which a speaker is provided for generating sounds of calling signals, and a vibrating device is provided for informing the receiver of calling signals without generating sounds. In such a device, since both of the speaker and the vibrating device are mounted in the acoustic device, the device is increased in size and weight, and in manufacturing cost.
In recent years, there is proposed a multifunction acoustic device in order to remove the above described disadvantages. The multifunction acoustic device comprises a speaker having a vibrating plate and a permanent magnet magnetically connected to a voice coil mounted on the vibrating plate of the speaker. The vibrating plate is vibrated at a high frequency of several 100 Hz to several KHz to produce sounds. The permanent magnet is independently vibrated at a low frequency of 10-100 Hz so as to inform the receiving of calling signals by the vibration of the case of the device, which is transmitted to the body of the user of the device.
FIG. 6 is a sectional view of a multifunction acoustic device disclosed in Japanese Utility Model Publication No. 2549375. The device comprises a spring plate 17 secured to a case 18, a pole piece 19 securely mounted on the spring plate 17 at the central portion of the spring plate, and a permanent magnet 20 mounted on the bottom of the case 18, surrounding the pole piece 19. An exciting coil 21 is secured to the permanent magnet 20 around the pole piece 19.
A diaphragm 16 is secured to the periphery of the case 18, and an armature 15 is fixed to the underside of the diaphragm 16. Thus, a magnetic circuit is formed by the pole piece 19, armature 15 and permanent magnet 20.
When a signal current of 2.1 KHz or 2.7 KHz is applied to the exciting coil 21, the diaphragm 16 is vibrated to produce sounds. When a current of 130 Hz is applied to the coil 21, the pole piece 19 is vibrated to vibrate the case, thereby informing a calling signal.
By properly setting the difference between compliances of the diaphragm 16 and the spring plate 17, the sounds and the oscillation frequency of the pole piece 19 can be changed.
In such a multifunction acoustic device, if there are variances in dimensional accuracy of manufactured devices, the vibration characteristic varies with the devices. In order to remove such a variance, it is necessary to increase the accuracy of products, which causes the manufacturing cost to increase.
In addition, it is difficult to manufacture devices so as to each have a desired vibration frequency, thereby reducing the yield of products.
An object of the present invention is to provide a multifunction acoustic device which may be manufactured so as to have a predetermined vibration frequency.
According to the present invention, there is provided a multifunction acoustic device comprising a cover, a diaphragm mounted in the cover for producing sounds, a vibrating assembly including a pole piece resiliently mounted in the cover so as to be vibrated, a voice coil provided for vibrating the diaphragm, a receiving portion formed on the vibrating assembly for receiving a mass adjusting material.
The receiving portion is a recess formed in the pole piece.
The recess is formed in the underside of the pole piece, and the cover has an opening corresponding to the recess.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.